U.S. patent number 7,821,475 [Application Number 11/846,734] was granted by the patent office on 2010-10-26 for image display apparatus.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Motomi Tsuyuki, Shoichi Yamazaki.
United States Patent |
7,821,475 |
Tsuyuki , et al. |
October 26, 2010 |
Image display apparatus
Abstract
The image display apparatus is capable of reducing moire fringe
when electric inverse-correction is performed on an image output to
an image display element. The apparatus includes an optical system
for observation of an image displayed on an image display element,
a processor performing distorting processing that electrically
provides to an input image a distortion in a direction inverse to
that of distortion as aberration generated by the optical system,
and a filter providing a low-pass filter effect to the image
observed through the optical system. When a first image region
including a first number of pixels in the input image is converted
into a second image region including a second number of pixels by
the distorting processing, the filter provides the low-pass filter
effect depending on the relationship between the first and second
numbers of pixels to the second image region.
Inventors: |
Tsuyuki; Motomi (Kawasaki,
JP), Yamazaki; Shoichi (Yokohama, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
39150752 |
Appl.
No.: |
11/846,734 |
Filed: |
August 29, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080055193 A1 |
Mar 6, 2008 |
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Foreign Application Priority Data
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Aug 31, 2006 [JP] |
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2006-236439 |
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Current U.S.
Class: |
345/7; 345/8;
359/629; 345/204 |
Current CPC
Class: |
G02B
27/017 (20130101); G02B 17/026 (20130101); G02B
27/46 (20130101); G02B 17/045 (20130101); G09G
2354/00 (20130101); G09G 2370/04 (20130101); G02B
2027/011 (20130101); G02B 2027/014 (20130101) |
Current International
Class: |
G09G
5/00 (20060101) |
Field of
Search: |
;345/7-9,32,204 ;348/115
;358/448 ;359/629-634 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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06-265815 |
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Sep 1994 |
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JP |
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2001-186442 |
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Jul 2001 |
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JP |
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Primary Examiner: Nguyen; Kimnhung
Attorney, Agent or Firm: Cowan, Liebowitz & Latman,
P.C.
Claims
What is claimed is:
1. An image display apparatus comprising: an image display element;
an optical system for observation of an image displayed on the
image display element; a processor which performs distorting
processing that electrically provides to an input image a
distortion in a direction inverse to that of distortion as
aberration generated by the optical system, and displays an image
subjected to the distorting processing on the image display
element; and a filter which provides a low-pass filter effect to
the image that is observed through the optical system, wherein,
when a first image region that includes a first number of pixels in
the input image is converted into a second image region that
includes a second number of pixels by the distorting processing,
the filter provides the low-pass filter effect depending on the
relationship between the first number of pixels and the second
number of pixels to the second image region that is observed
through the optical system.
2. An image display apparatus according to claim 1, wherein, when
the second number of pixels is less than the first number of
pixels, the filter provides to the second image region that is
observed through the optical system the low-pass filter effect
higher than that when the second number of pixels is more than the
first number of pixels.
3. An image display apparatus according to claim 1, wherein, when
the second number of pixels is less than the first number of
pixels, the low-pass filter effect provided by the filter to the
second image region that is observed through the optical system
becomes higher as the difference between the first number of pixels
and the second number of pixels increases.
4. An image display apparatus according to claim 1, wherein the
filter provides to each of a plurality of the second image regions
the low-pass filter effect that changes depending on the
relationship between the first number of pixels and the second
number of pixels.
5. An image display apparatus according to claim 1, wherein the
filter optically provides the low-pass filter effect to an image
formed with a light flux from the image display element.
6. An image display apparatus according to claim 1, wherein the
filter provides the low-pass filter effect by electric processing
to an image displayed in the image display element.
7. An image display apparatus according to claim 1, wherein the
image displayed on the image display element after the distorting
processing is a distorted image having a rotationally asymmetric
shape.
8. An image display system comprising: an image display apparatus
according to claim 1; and an image supplying apparatus which
supplies image information to the image display apparatus.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an image display apparatus such as
a head-mounted display and a projector, which enlarges an original
image displayed on an image display element and displays an
enlarged image thereof.
A head-mounting type image display apparatus (head-mounted display:
hereinafter, referred to as an "HMD") has been used which enlarges
an image (original image) displayed on an image display element
such as a CRT and an LCD and displays the enlarged image thereof
through an optical system.
Since this HMD is mounted on a head of an observer, reductions in
size and weight thereof are required. On the other hand, it is
desired that the HMD have a good optical performance and can
provide an enlarged image as large as possible.
However, when the optical system is made small, distortion and
axial chromatic aberration are generated, which makes it difficult
to achieve a good optical performance. On the contrary, when the
optical system is designed to reduce generation of the distortion
and various aberrations, it is difficult to reduce the size of the
optical system. Therefore, an HMD has been proposed which
electrically corrects the distortion and the chromatic aberration
of the optical system to reduce a load for aberration corrections
of the optical system, thereby enabling miniaturization of the
HMD.
For example, an HMD has been disclosed in Japanese Patent Laid-Open
No. 6-265815 which improves an apparent resolution by synthesizing
images displayed in two liquid crystal panels on a retina of an
observer. This HMD electrically distorts (corrects) the images
displayed on the liquid crystal panels such that an influence of
the distortion generated by an optical system is canceled.
Moreover, an HMD has been disclosed in Japanese Patent Laid-Open
No. 2001-186442 which outputs right and left video signals while
temporally alternately switching them to one image display element,
and causes image light to alternately enter into right and left
eyes in synchronization with the switching of the right and left
video signals. This HMD electrically distorts (corrects) the right
and left video signals such that distortions generated by right and
left optical systems are respectively canceled.
Performing such electric distorting correction on the image output
to the image display element like the HMDs disclosed in the
above-mentioned publications so as to cancel the distortion of the
optical system can cause the observer to view an image with reduced
distortion. The electric distorting correction is hereinafter
referred to as the "inverse-correction", and an image to which the
inverse-correction was made is referred to as an
inversely-corrected image.
However, when displaying the inversely-corrected image on the image
display element with a high pixel number, moire fringe
(interference fringe) generated by interference between
regularly-arranged pixels and the distorted image may be observed.
Therefore, even if the resolution of the image display apparatus is
improved, the moire fringe will provide discomfort to the
observer.
SUMMARY OF THE INVENTION
The present invention provides an image display apparatus capable
of reducing generation of the moire fringe when the electric
inverse-correction is performed on an image output to the image
display element.
According to an aspect, the present invention provides an image
display apparatus including an image display element, an optical
system for observation of an image displayed on the image display
element, a processor which performs distorting processing that
electrically provides to an input image a distortion in a direction
inverse to that of distortion as aberration generated by the
optical system, and displays an image subjected to the distorting
processing on the image display element, and a filter which
provides a low-pass filter effect to the image that is observed
through the optical system. When a first image region that includes
a first number of pixels in the input image is converted into a
second image region that includes a second number of pixels by the
distorting processing, the filter provides the low-pass filter
effect depending on the relationship between the first number of
pixels and the second number of pixels to the second image region
that is observed through the optical system.
According to another aspect, the present invention provides n image
display system including the above-described image display
apparatus and an image supplying apparatus which supplies image
information to the image display apparatus.
Other objects and aspects of the present invention will become
apparent from the following description and the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a cross-sectional view showing the configuration of an
optical system that is Embodiment 1 of the present invention.
FIG. 1B is a figure showing an inversely-corrected image in
Embodiment 1.
FIG. 1C is a figure showing the intensity of a low-pass filter
effect in Embodiment 1.
FIG. 2A is a cross-sectional view showing the configuration of an
optical system that is Embodiment 2 of the present invention.
FIG. 2B is a figure showing an inversely-corrected image in
Embodiment 2.
FIG. 3A is a cross-sectional view showing the configuration of an
optical system that is Embodiment 3 of the present invention.
FIG. 3B is a figure showing an inversely-corrected image in
Embodiment 3.
FIG. 4A is a cross-sectional view showing the configuration of an
optical system that is Embodiment 4 of the present invention.
FIG. 4B is a figure showing an inversely-corrected image in
Embodiment 4.
FIG. 5A is a cross-sectional view showing the configuration of an
optical system that is Embodiment 5 of the present invention.
FIG. 5B is a figure showing an inversely-corrected image in
Embodiment 5.
FIG. 6A is a figure showing an input image in a basic concept of
embodiments of the present invention.
FIG. 6B is a figure showing an inversely-corrected image for the
input image of FIG. 6A.
FIG. 6C is a figure showing an observed image in the basic concept
of embodiments of the present invention.
FIG. 6D is a figure showing region splitting of the input image in
the basic concept of embodiments of the present invention.
FIG. 6E is a figure showing an inversely-corrected image for the
input image of FIG. 6D.
FIG. 6F is a figure showing a region splitting of the input image
in the basic concept of embodiments of the present invention.
FIG. 6G is a figure showing an inversely-corrected image for the
input image of FIG. 6F.
FIG. 6H is a figure showing a region splitting of the input image
in the basic concept of embodiments of the present invention.
FIG. 6I is a figure showing a region splitting of the
inversely-corrected image in the basic concept of embodiments of
the present invention.
FIG. 7 is a figure showing a region splitting of the input image in
Embodiments 1 to 5 of the present invention.
FIG. 8A is a figure showing an example of an HMD on which the
present invention is applied.
FIG. 8B is a figure showing an example of a projector on which an
embodiment of the present invention is applied.
FIG. 9A is a figure showing an example of a low-pass filter effect
achieved by an embodiment of the present invention.
FIG. 9B is a front view showing the relationship between an optical
low-pass filter and an image display element in the present
invention.
FIG. 9 C is a side view showing the relationship between the
optical low-pass filter and the image display element in the
present invention.
DESCRIPTION OF THE EMBODIMENTS
Embodiments of the present invention will hereinafter be described
with reference to the accompanying drawings.
First of all, a basic concept of embodiments of the present
invention will be explained by using FIGS. 6A to 6I. When light
emerging from an image display element through an optical system is
observed by an observer, it is preferable to be able to show a good
image that does not distort as shown in FIG. 6C.
However, when the optical system has distortion as aberration,
displaying an image without distortion on the image display element
causes the observer to observe a distorted image as shown in FIG.
6A. Therefore, in this embodiment, as shown in FIG. 6B, an image on
which electric distorting processing (or electric distorting
correction, hereinafter referred to as "inverse-correction") was
made so as to cancel the distortion of the optical system is output
to the image display element. That is, an image to which a
distortion was provided in a direction inverse to that of the
distortion as aberration generated by the optical system is output
to the image display element.
The observer can observe an image with reduced distortion or
without distortion as shown in FIG. 6C by observing through the
optical system the image after the inverse-correction. An image on
which the inverse-correction was made is referred to as an
inversely-corrected image.
However, as mentioned above, when the distorted image is displayed
on the image display element with a high pixel number, moire fringe
may be generated. Therefore, in this embodiment, a low-pass filter
effect is provided to the image observed through the optical
system.
The wording "a low-pass filter effect is provided to the image
observed through the optical system" includes providing an optical
low-pass filter effect to an image formed with light rays emerging
from the image display element, as described later. Furthermore, it
also includes providing a low-pass filter effect by electric
processing to an image output to (displayed on) the image display
element.
In considering the low-pass filter effect, in this embodiment, H
(horizontal).times.V (vertical) pixels of an input signal of the
image (input image) and image display element is used as the base.
The resolution of the image input to the image display element is
defined as: H(horizontal).times.V(vertical) pixels=X pixels.times.Y
pixels.
The input image is divided into plural regions (image regions) as
shown in FIG. 6D, and one thereof is defined as a region R (m
pixels (horizontal).times.n pixels (vertical)). In this case, the
region (first image region) R is converted by the
inverse-correction into a region (second image region) S with
distortion as shown in FIG. 6E, and then is output to the image
display element. In this case, the maximum display pixel number of
H.times.V that shows the region S is defined as M pixels.times.N
pixels. That is, the region R (m pixels.times.n pixels) of the
input image is converted by the inverse-correction into the region
S (M pixels.times.N pixels), which produces an output image.
Next, the "low-pass filter effect" in this embodiment will be
defined.
When an input image (monochrome line image) having the size for
being displayed in the entire region on the image display element
and including alternating white and black lines each being
one-pixel line in the H direction is inversely corrected, an output
image is generated in which the white and black lines have a
certain distortion. In this case, when observing the image display
element, it can be confirmed that each pixel of the image display
element is resolved (a spatial frequency at this time is defined as
E).
However, since the output image is output in a state in which the
white and black lines are distorted, the pixels of the image
display element interfere with the output image, which generates
the moire fringe in some regions.
Moreover, the white and black lines after the inverse-correction
are displayed as non-straight lines. Therefore, when observing this
inverse-corrected monochrome line image through the optical system,
the white and black lines are observed as step-like lines (for
example, white lines including shading) in addition to the moire
fringe. This is called "aliasing".
The low-pass filter effects include an "electric low-pass filter
effect" that reduces the resolution of an inversely-corrected image
when the image is output to the image display element.
More specifically, when the inversely-corrected monochrome line
image is output, one pixel (A pixel) outputting a certain signal is
noted in a region to be provided with the low-pass filter effect.
In this case, a comparator, a calculator, and a substitutor are
provided. The comparator compares the A pixel with a circumference
pixel (B pixel) existing in the vicinity thereof. The calculator
calculates an additional value according to the comparison result.
The substitutor substitutes the A pixel and the circumference pixel
B with the additional value. As a result, generation of the moire
fringe and aliasing can be reduced in observation of the image
output to the image display element through the optical system,
while reducing the resolution of the white and black lines.
Furthermore, the low-pass filter effects also include an "optical
low-pass filter effect". More specifically, the optical low-pass
filter effect is obtained by a method of changing a ray-splitting
width using birefringence of a liquid crystal element and a method
of using birefringence of an optical material such as crystal or
lithium niobate which is located at an arbitrary position between
the liquid crystal element and the optical system. Furthermore, it
is obtained by a method of using an optical element with a
diffraction grating.
These optical low-pass filter effects correspond to an effect that
optically changes a spatial frequency E' of the image displayed on
the image display element (resolution of the image display element)
into a spatial frequency F'. The spatial frequency F' represents,
when birefringence of a liquid crystal element is used, a
resolution of an image formed with light rays emerging from the
liquid crystal element. Furthermore, the spatial frequency F'
represents, when an optical material such as crystal is used, a
resolution immediately after light rays emerging from the image
display element passes the optical material. There are some cases
where the resolution is not reduced even though the low-pass filter
effect is provided. However, it can be said that the low-pass
filter effect is also effective in those cases.
In particular, the optical material or the optical element having a
diffraction grating is located at a position near the image display
element or bonded on a cover glass having a role to protect a
light-receiving surface of the image display element. As a result,
a good low-pass filter effect can be obtained for the moire fringe
and aliasing generated in the inversely-corrected image.
In this embodiment, the electric and optical low-pass filter
effects are set as follows according to the relationship between
the number of pixels in the region R shown in FIG. 6D showing a
region splitting of the input image and the number of pixels in the
region S shown in FIG. 6E showing an inversely-corrected image for
the input image shown in FIG. 6D.
The setting in the H direction is as follows:
For 1.ltoreq.M/m, the low-pass filter effect is set to be an effect
multiplying the spatial frequency of the output image by a value
from 1 to 1/1.5;
For 0.8.ltoreq.M/m<1, the low-pass filter effect is set to be an
effect multiplying the spatial frequency of the output image by a
value from 1 to 1/2.3; and
For M/m<0.8, the low-pass filter effect is set to be an effect
multiplying the spatial frequency of the output image by a value
from 1/1.4 to 1/2.5.
On the other hand, the setting in the V direction is as
follows:
For 1.ltoreq.N/n, the low-pass filter effect is set to be an effect
multiplying the spatial frequency of the output image by a value
from 1 to 1/1.5;
For 0.8.ltoreq.N/n<1, the low-pass filter effect is set to be an
effect multiplying the spatial frequency of the output image by a
value from 1 to 1/2.3; and
For N/n<0.8, the low-pass filter effect is set to be an effect
multiplying the spatial frequency of the output image by a value
from 1/1.4 to 1/2.5.
That is, in the case where the number of pixels (M or N) in the
region S after the inverse-correction is less than that (m or n) in
the region R in the input image, a higher low-pass filter effect is
provided to the region S as compared with the case where the number
of pixels in the region S is equal to or more than that in the
region R.
In the case where the number of pixels in the region S is less than
that in the region R, the low-pass filter effect provided to the
region S becomes higher as the difference between the number of
pixels in the region S and that in the region R increases (that is,
as the number of pixels in the region S less than that in the
region R reduces).
Under the above-mentioned setting condition, one with a higher
low-pass filter effect is selected from the H and V directions as
the direction in which the low-pass filter effect is provided to
the region S, and the optical or electric low-pass filter effect is
provided to the region S. This can reduce the moire fringe and the
aliasing, thereby enabling to provide a good image.
When the input image and the image display element have quite a lot
of number of pixels, even if the low-pass filter effect worsens the
spatial frequency in some regions, the observer hardly minds the
reduced moire fringe and aliasing. Furthermore, the low-pass filter
effect is changed for each region of the output image. This can
provide an image to the observer without reduction of the
resolution in the region where the reduction thereof is not
particularly needed.
Although the observer will observe the region with a high
resolution and the region with a slightly reduced resolution at the
same time, the observer does not mind a small difference of the
resolutions. That is, the observer prefers the observation of an
image with reduced distortion, moire fringe and aliasing to that of
an image with a wholly reduced resolution. Moreover, the electric
inverse-correction for correcting the distortion of the optical
system reduces a load for the aberration correction by the optical
system, thereby enabling a contribution to miniaturization of the
optical system and correction of aberrations other than the
distortion.
Although the region R and the region S were determined based on the
reference coordinates (H direction.times.the V direction) so far,
the regions may be determined on the basis of arbitrary
coordinates.
FIGS. 6D and 6E show a case where the region R of the input image
is partitioned in parallel with the reference coordinates (H
direction.times.V direction). However, as shown in FIG. 6G, the
region S' of the image output (inversely-corrected image) to the
image display element may be a region partitioned in parallel with
the reference coordinates (H direction.times.V direction). In this
case, the region R' of the input image is as shown in FIG. 6F.
When the low-pass filter effect is provided for the regions
parallel to the above-mentioned reference coordinates in the input
image, the numbers of pixels (n pixels) in plural
H-direction-regions R1 to R5 divided in the V direction may be
different from each other as shown in FIG. 6H. On the other hand,
when the low-pass filter effect is provided for the regions
parallel to the above-mentioned reference coordinates in the output
image (inversely-corrected image), the number of M pixels and the
number of N pixels in plural regions S'' may be different from each
other as shown in FIG. 6I.
Furthermore, although the low-pass filter effect may be considered
for the regions partitioned in parallel with the reference
coordinates in one of the input image and the output image as
described so far, it may be considered for a distorted region in
both the images.
An example of changing the low-pass filter effect for each region
by using the optical material is shown in FIGS. 9A to 9C.
FIG. 9A shows the results obtained by dividing the output image
into plural regions (five regions in this example) in the V
direction and applying them to the above-mentioned setting
condition of the low-pass filter effect. In this case, as shown in
FIG. 9B, a low-pass filter 90 formed of crystal that is the optical
material is disposed on an image display element 10 or at a
position close thereto to obtain a low-pass filter effect suitable
for each region.
FIG. 9C shows various examples of the crystal low-pass filter 90
shown in FIG. 9B provided for the image display element 10 when
viewed from their sides.
As shown in this figure, the thickness of the crystal is changed
depending on the desired intensity of the low-pass filter effect.
For example, when viewed from the side, the crystal is cut out in a
step-like shape, in an obliquely linear shape, or in a curved
shape.
The curved cutout surface is formed as a rotationally symmetric
surface or a rotationally asymmetric surface according to the
amount of the inverse-correction of the output image.
As shown at the right of FIG. 9C, the crystal may be cut out so
that it is disposed only for some regions where the low-pass filter
effect are required. In this case, the low-pass filter will not be
provided for the region where the crystal is not disposed. However,
this case is also included in embodiments of the present
invention.
The image display apparatus that performs the electric
inverse-correction of the input image and provides the low-pass
filter effect, described above, can be embodied as an HMD shown in
FIG. 8A and a projector shown in FIG. 8B. In addition, the image
display apparatus is not limited to these HMD and projector, and
can be embodied as other various image display apparatuses.
In FIG. 8A, reference numeral 10 denotes an image display element
such as a liquid crystal panel. Reference numeral 60 denotes an
ocular optical system that introduces a light flux from the image
display element 10 to an eye E of an observer. The right figure of
FIG. 8A shows the appearance of this HMD in which an output image
(inversely-corrected image) obtained by inversely correcting an
input image is displayed on the image display element 10.
The image display element 10 is electrically connected with a drive
circuit (processor) 200. An image supplying apparatus 210 such as a
personal computer, a DVD player, and a TV tuner is electrically
connected with the drive circuit 200. The image supplying apparatus
210 supplies image information to the image display apparatus. The
drive circuit 200 performs processing for the inverse-correction on
the image (input image) input from the image supplying apparatus
210, and then displays the inversely-corrected image on the image
display element 10.
When the electric low-pass filter effect is provided to the
inversely-corrected image, the image subjected to that processing
is displayed on the image display element 10. The image display
apparatus and the image supplying apparatus 210 constitute an image
display apparatus.
In FIG. 8B, reference numeral 10 denotes an image display element,
and reference numeral 100 denotes a projection optical system that
projects a light flux from the image display element 10 onto a
screen 70. The lower figure of FIG. 8B shows the appearance of this
projector in which an output image (inversely-corrected image)
obtained by inversely correcting an input image is displayed on the
image display element 10.
Although not shown, this projector is also connected with the image
supplying apparatus shown in FIG. 8A, thereby constituting an image
display system.
Embodiment 1
FIG. 1A shows the configuration of a display optical system for an
HMD that is Embodiment 1 of the present invention.
An optical element 1 is a prism member having three or more optical
surfaces that are a surface A (S2, S4, S6), a surface B (S3, S7),
and a surface C (S5) on a transparent medium whose refractive index
is larger than 1.
An optical element 2 is a prism member having two optical surfaces
that are surfaces S8 and S9 on a transparent medium whose
refractive index is larger than 1.
A lens 3 has surfaces S10 and S11, and a lens 4 has surfaces S12
and S13. These lenses 3 and 4 are cemented with each other at the
surfaces S11 and S12.
A lens 5 has surfaces S14 and S15, and a flat plate 6 has surfaces
S16 and S17. A decentered cylindrical lens 8 has a surface S18 and
a surface S19 (identical with a surface S23). The surface S19 (S23)
of this cylindrical lens 8 is a transmitting/reflecting surface
(half mirror). Reference numeral 10 denotes an image display
element. A reflective liquid crystal panel is used as the image
display element 10 in this embodiment. Surfaces S20 (S22) and S21
are surfaces of a cover glass provided for the image display
element 10 (hereinafter referred to as the LCD 10). Reference
numeral S21 denotes an image-displaying surface of the LCD 10.
Other elements than the LCD 10, such as a CRT, a transmissive
liquid crystal panel, and an electroluminescent element, can be
used as the image display element 10. This is applied to the
embodiments described later.
A planar illumination light source is used for an illumination
light source 30 (surface SI) in this embodiment. When light emitted
from the illumination light source 30 enters the LCD 10, the
cylindrical lens 8 has the role as an illumination optical
system.
Reference numerals 7 and 14 denote polarizing plates. The lenses 3
and 4 are cemented with each other as described above. All optical
surfaces other than those of these cemented lenses 3 and 4 and the
cylindrical lens 8 have a plane-symmetric shape with respect to the
sheet of FIG. 1A (yz-cross section) which is the only plane of
symmetry.
The light emitted from the illumination light source 30 is
transmitted through the polarizing plate 14 to be converted into
linearly-polarized light, and then is reflected on a surface S23 of
the cylindrical lens 8 to proceed to the LCD 10. The light
obliquely entering the LCD 10 is reflected by the image-displaying
surface S21 thereof in an oblique direction to enter the
cylindrical lens 8 from its surface S19, and then emerges from its
surface S18. The light is then transmitted through the polarizing
plate 7 to enter the flat plate 6 from its surface S17, and then
emerges from its surface S16 to proceed to the lens 5.
At this time, since the polarization direction of the
linearly-polarized light entering the polarizing plate 14 is
rotated in the LCD 10, the polarizing plate 7 is set so as to
transmit that linearly-polarized light whose polarization direction
is rotated.
When the polarization direction of the linearly-polarized light
transmitted through the polarizing plate 7 shifts by 90.degree. to
the polarization direction of the linearly-polarized light
transmitted through the polarizing plate 14 according to the
polarization rotation angle of 90.degree. by the LCD 10, the light
converted into linearly-polarized light by the polarizing plate 14
may be transmitted through the surface S23 without being reflected
thereon and become ghost light. However, this ghost light can be
cut by the polarizing plate 7, so that entrance of the ghost light
into observer's eye can be prevented.
The light entering the lens 5 from the surface S15 emerges from the
surface S14, and then enters the lens 4 from the surface S13. The
light is transmitted through the surface S12 of the lens 4 and the
surface S11 of the lens 3, and then emerges from the surface S10 to
proceed to the optical element 2.
The light entering the optical element 2 from the surface S9 is
transmitted through the surface S8 of the optical element 2 and the
surface S7 of the optical element 1 to enter the optical element 1.
The surface S8 of the optical element 2 is cemented with the
surface S7 of the optical element 1.
In the optical element 1, the light entering from the surface B
(S7) is reflected by the surface A (S6) to be introduced to the
surface C (S5). The light incident on the surface C (S5) is
subjected to a returning reflection in which the light is reflected
to the opposite side (the returning reflection will be described
later), and then proceeds in the opposite direction to that of
light before the returning reflection on the surface C. The light
reflected on the surface C (S5) is again reflected on the surface A
(S4), further again reflected on the surface B (S3) and then
emerges from the surface A (S2) to proceed to an exit pupil S1.
At this time, rays from ends of the image-displaying surface (S21)
intersect with each other in the optical element 1 to form an
intermediate image-forming surface of the image displayed on the
image-displaying surface. In this embodiment, the intermediate
image is formed between the reflection points on the surfaces S4
and S5. However, the intermediate image needs not to be formed
therebetween.
This embodiment has a so-called ocular optical system part that
introduces the light flux passing through the intermediate
image-forming surface to the exit pupil S1 as a parallel light
flux. In order to facilitate the aberration correction in the
ocular optical system part, it is preferable that the intermediate
image is formed such that it has an appropriate curvature or an
appropriate astigmatic difference depending on the generation
situation of field curvature or astigmatism in the ocular optical
system part.
The optical surfaces from the surface S5 for reflection of the
light flux to the surface S2 for emergence thereof correspond to
the ocular optical system part, and part of the optical element 1
other than the above optical surfaces and an optical system
disposed between the optical element 1 and the cover glasses of the
LCD 10 correspond to a relay optical system part. The surface S3
when acting as the final reflecting surface serves as a concave
mirror having a very strong power with respect to the surface S2
when acting as an emergent surface. Therefore, it is difficult to
completely correct the aberration in the ocular optical system
part.
For this reason, in this embodiment, an intermediate image is
formed on the intermediate image-forming surface such that the
aberration in the ocular optical system part is canceled by the
relay optical system part. As a result, the quality of a
finally-observed image can be improved.
When the reflection on the surface S4 is an internal total
reflection in the optical element 1, loss of light amount is
reduced, which is preferable. When the reflections on at least a
region used by the light flux emerging from the surface S2 and the
light flux reflected on the surface S4 are internal total
reflections, a brightness at the same level as that in a case where
all reflections are internal total reflections is secured while
raising the design freedom of the optical system.
In this case, the reflection on the surface S4 which is not an
internal total reflection is a reflection by a reflective film.
Moreover, the reflection on the surface S5 is a reflection by a
reflective film.
In the optical element 1, the light passes the surfaces in the
following order: the surface B.fwdarw.the surface A.fwdarw.the
surface C.fwdarw.the surface A.fwdarw.the surface B (.fwdarw.the
surface A). That is, the light traces an optical path from the
reflecting surface C that serves as the boundary to the final
reflecting surface B, the optical path being inverse to that before
the boundary, and thus forms a first path: the surface B.fwdarw.the
surface A.fwdarw.the surface C, and a second (returning) path: the
surface C.fwdarw.the surface A.fwdarw.the surface B.
The reflection that switches the optical path from the first path
to the returning path like that on the surface C is referred to as
a "returning reflection", and the surface having such a returning
reflection function is referred to as a "returning surface". Thus,
a long optical length can be contained in the small optical element
1 by folding the optical path with the plural decentered reflecting
surfaces A, B and C to duplicate the first and returning paths. As
a result, the size of the entire display optical system shown in
FIG. 1A can be reduced.
When a ray impinging on the returning surface is reflected thereby
to form a predetermined angle of .theta. before and after the
reflection, the angle .theta. is preferable to satisfy the
following expression: |.theta.|<60.degree. (1)
If the angle .theta. does not satisfy the conditional expression
(1), the optical path (returning path) after the returning
reflection does not retrace the first path, and thus the optical
path becomes a zigzag optical path rather than a reciprocating
optical path. As a result, the size of the optical element 1 may
increase.
Furthermore, the angle .theta. preferably satisfies a condition of
the following expression: |.theta.|<30.degree. (2)
If the angle .theta. does not satisfy the conditional expression
(2), the overlapping degree of the first and returning paths
becomes small though the returning path retraces the first path.
Therefore, the size of the optical element 1 becomes large, which
may make it difficult to miniaturize the entire display optical
system.
Furthermore, if the angle .theta. satisfies a condition of the
following expression, the entire display optical system can be more
miniaturized. |.theta.|<20.degree. (3)
A numerical example of the display optical system of this
embodiment is shown in Table 1.
In a conventional system definition that does not correspond to a
decentered system, each surface is defined by a coordinate system
(surface vertex coordinate system) based on the vertex of each
surface. That is, a z-axis is defined as an optical axis, a
yz-cross section is defined as a conventional generatrix cross
section (meridional cross section), and an xz-cross section is
defined as a directrix cross section (sagittal cross section).
However, since the display optical system of this embodiment is a
decentered system, a local generatrix cross section and a local
directrix cross section that correspond to the decentered system
are newly defined here.
When a ray passing through a position corresponding to the center
of the inversely-corrected image displayed on the image display
element and the center of the exit pupil is defined as a central
field-angle principal ray, a cross section including an incident
ray portion and an emergent ray portion of the central field-angle
principal ray at a hit point of the central field-angle principal
ray on each surface is defined as the local generatrix cross
section.
Moreover, a cross section including the hit point of each surface
and vertical to the local generatrix cross section and parallel to
the directrix cross section of the surface vertex coordinate system
(that is, a usual directrix cross section) is defined as the local
directrix cross section.
The curvature of each surface in the vicinity of the hit point of
the central field-angle principal ray is calculated, wherein the
curvature radius in the local generatrix cross section of each
surface is defined as ry, and the curvature radius in the local
directrix cross section is defined as rx.
Hereinafter, how to see the optical data in Table 1 will be
explained. This is the same in other embodiments described
later.
Item SURF shown at the most left in Table 1 represents the surface
number (i of Si). Items X, Y, and Z represent the location (x, y,
z) of the vertex of each surface in the coordinate system having
the origin (0, 0, 0) located at the center of the first surface S1,
the y- and z-axes shown in the figure, and the x-axis perpendicular
to the sheet of the figure. Item A represents a rotation angle "a"
(degrees) of each surface around the x-axis, which is positive in
the counterclockwise direction in the figure.
Item Typ represents types of surface shape. SPH represents a
spherical surface, FFS represents a rotationally asymmetric
surface, and CYL represents a cylindrical lens surface having a
refractive power only in the generatrix cross section. The
rotationally asymmetric surface in this embodiment is represented
by a conditional expression of FFS listed below. YTO shows that the
generatrix cross section is represented by the aspheric surface
conditional expression listed below and the directrix section is a
plane (rx=.infin.).
The item of R represents the curvature radius of each surface. For
the cylindrical lens surface, the value of the curvature radius ry
on the generatrix cross section is listed.
.times. ##EQU00001##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times..times-
..times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times. ##EQU00001.2##
The value described in the field of Typ next to FFS represents that
the surface shape is a rotationally asymmetric shape corresponding
to an aspheric surface coefficient k and c** that are described
under the table. However, the value of c** that is not described is
0.
Nd and .nu.d respectively represent the refractive index and the
Abbe number of the medium forming the surface in the d-line
wavelength. The change in signs of the refractive index Nd shows
that the light is reflected on the surface. When the medium is an
air layer, only the refractive index Nd is described as 1.0000 and
the Abbe number .nu.d is omitted.
The unit of length in Table 1 is mm. Therefore, the optical system
shown in Table 1 is a display optical system that displays an image
whose size is about 18 mm.times.14 mm and horizontal field angle is
60.degree. at the infinite position in the direction of the
z-axis.
In this embodiment, an extremely large distortion is generated by
the optical system. Therefore, an image subjected to the electric
distorting processing (inverse-correction) in the direction inverse
to that of the distortion generated by the optical system is output
to the image display element.
In this embodiment, the input image is divided into 8.times.8
regions in the H and V directions as shown in FIG. 7. This is the
same in other embodiments described later.
In this embodiment, the number of pixels of the input image is the
same as that of the image display element. This is the same in
other embodiments described later.
The output image (inversely-corrected image) obtained by inversely
correcting the input image (FIG. 7) is shown in FIG. 1B. The
calculation results of the low-pass filter effect for each of
8.times.8 regions in the output image distorted as shown in FIG. 1B
are shown in FIG. 1C, the calculation being performed according to
the above-mentioned setting condition of the low-pass filter
effect.
FIG. 1C shows a region where the low-pass filter effect is high, a
region where the low-pass filter effect is middle, and a region
where the low-pass filter effect is low.
Thus, in this embodiment, the distortion is not corrected by the
optical system, so that the optical system can be configured so as
to contribute to corrections of various aberrations other than the
distortion and to miniaturization of the optical system. This
embodiment achieves a display optical system (that is, an image
display apparatus) having an extremely good optical performance and
thereby enabling to provide an image with reduced distortion while
its size is small.
Furthermore, employing the configuration capable of providing an
adequate low-pass filter effect for each region while distorting
the image output to the image display element can cause the
observer to observe a good image with reduced distortion, moire
fringe and aliasing when the observer observes the image display
element through the optical system.
Moreover, in this embodiment, at least one surface of the optical
system is formed as a decentered surface with respect to the rays
from the image display element 10. Therefore, miniaturization of
the optical system can be achieved.
Furthermore, in this embodiment, since at least one surface of the
optical system is formed as a rotationally asymmetric surface, a
further miniaturization of the optical system and suppression of
various aberrations generated in the optical system (in particular,
chromatic aberration of magnification and axial chromatic
aberration) can be achieved.
Moreover, in this embodiment, the image inversely corrected and
displayed on the image display element 10 is a distorted image
having a rotationally asymmetric shape. As a result, the
contribution of the optical system to various aberration
corrections is reduced and thereby the power setting of the optical
system is not unreasonable, so that a large tolerance for the
surfaces of the optical system can be obtained, which can
facilitate manufacturing of the optical system.
In this embodiment, although the case where the number of pixels of
the input image is the same as that of the image display element
was described, these may be different from each other. In this
case, the intensity of the low-pass filter effect may be set
according to the setting condition for the low-pass filter effect,
the setting condition corresponding to the original difference
between the number of pixels of the input image and that of the
image display element. This is the same in other embodiments
described later.
TABLE-US-00001 TABLE 1 SURF X Y Z A R typ Nd .nu.d 1 0.000 0.000
0.000 0.000 0.0000 SPH 1.0000 0.0 2 0.000 9.365 21.886 -0.529
-284.2114 FFS1 1.5300 55.8 3 0.000 -2.638 34.455 -31.052 -72.0536
FFS2 -1.5300 55.8 4 0.000 9.365 21.886 -0.529 -284.2114 FFS1 1.5300
55.8 5 0.000 30.738 47.306 48.060 -189.3367 FFS3 -1.5300 55.8 6
0.000 9.365 21.886 -0.529 -284.2114 FFS1 1.5300 55.8 7 0.000 -2.638
34.455 -31.052 -72.0536 FFS2 1.5300 55.8 8 0.000 -2.638 34.455
-31.052 -72.0536 FFS2 1.5300 55.8 9 0.000 -5.791 39.117 -46.389
-56.9404 FFS4 1.0000 10 0.000 -7.538 37.525 -53.721 18.2091 SPH
1.4875 70.2 11 0.000 -16.105 43.813 -53.721 -21.5267 SPH 1.7618
26.5 12 0.000 -17.556 44.878 -53.721 66.0282 SPH 1.0000 13 0.000
-18.692 44.573 -50.460 20.6510 FFS5 1.5300 55.8 14 0.000 -32.859
25.439 -88.990 -118.4382 FFS6 1.0000 15 0.000 -49.433 29.812
-45.448 .infin. SPH 1.5230 58.6 16 0.000 -50.288 30.654 -45.448
.infin. SPH 1.0000 17 0.000 -32.898 51.561 -24.427 25.6080 CYL
1.7618 26.5 18 0.000 -30.463 55.740 -38.300 21.8260 CYL 1.0000 19
0.000 -38.215 64.167 -66.742 .infin. SPH 1.5500 52.0 20 0.000
-38.858 64.443 -66.742 .infin. SPH 1.0000 21 0.000 -38.858 64.443
-66.742 0.0000 SPH 1.0000 0.0 FFS1 c1: 4.7708e+001 c5: -2.2635e-003
c6: -2.6964e-004 c10: -3.5045e-006 c11: -1.8961e-005 c12:
-2.5872e-007 c13: -3.5080e-007 c14: -1.8809e-007 c20: -8.5708e-010
c21: -5.5035e-010 c22: -4.8677e-010 c23: 1.7886e-011 c24:
2.5426e-011 c25: 1.2297e-011 c26: 6.2276e-012 FFS2 c1: -8.0283e-001
c5: -1.3225e-003 c6: -3.2740e-004 c10: -1.0438e-005 c11:
-4.7937e-007 c12: -5.0068e-008 c13: -6.2302e-008 c14: 4.5234e-008
c20: 1.9842e-009 c21: -5.0837e-010 c22: 1.1409e-009 c23:
1.8477e-011 c24: -1.7819e-011 c25: 1.2831e-011 c26: -2.0655e-011
FFS3 c1: 2.6924e+001 c5: 2.4531e-004 c6: -1.2389e-003 c10:
-4.7294e-005 c11: 3.6501e-005 c12: 2.1833e-006 c13: -2.0621e-006
c14: 1.3400e-006 c20: -3.4331e-008 c21: 2.1762e-008 c22:
-5.5534e-009 c23: -2.7291e-010 c24: -2.2240e-010 c25: -2.8204e-010
c26: 2.0643e-011 FFS4 c1: -2.0112e+000 c5: -1.1439e-003 c6:
-7.0182e-003 c10: 6.6323e-005 c11: 3.7827e-005 c12: -3.0764e-007
c13: -1.2255e-007 c14: 2.8074e-007 c20: -4.8304e-008 c21:
-6.8627e-009 c22: 1.4540e-008 c23: 1.9275e-010 c24: -2.0887e-010
c25: -6.5050e-010 c26: 1.3565e-010 FFS5 c1: 8.3170e-001 c5:
2.2565e-003 c6: -1.7932e-003 c10: 4.9769e-005 c11: 5.8833e-005 c12:
-1.8053e-006 c13: 3.0888e-007 c14: -2.4892e-006 c20: -1.1149e-008
c21: -5.0541e-008 c22: 3.6852e-008 c23: 1.3332e-009 c24:
-1.1902e-009 c25: -7.4560e-011 c26: 9.7807e-009 FFS6 c1:
5.0873e-001 c5: 1.7979e-003 c6: 1.0845e-003 c10: -4.0100e-005 c11:
-2.0713e-004 c12: 3.9779e-006 c13: 1.4457e-006 c14: -2.9702e-007
c20: -5.7229e-009 c21: 2.9933e-008 c22: -3.2629e-008 c23:
-5.6700e-011 c24: -1.7802e-010 c25: -2.0885e-010 c26:
-3.8998e-011
The optical data of the illumination light source 30 and polarizing
plate 14 are not shown in Table 1. This is the same in other
embodiments described later.
Embodiment 2
FIG. 2A shows the configuration of a display optical system for an
HMD that is Embodiment 2 of the present invention. An optical
element 1 is a prism member having three or more optical surfaces
on a transparent media whose refractive index is larger than 1. An
optical element 2 is a prism member having two optical surfaces on
a transparent media whose refractive index is larger than 1.
Reference numerals 3, 4, 5, and 9 denote lenses each having two
surfaces. Reference numeral 8 denotes a decentered cylindrical
lens. Reference numeral 10 denotes an image display element
(reflective LCD).
A surface of the cylindrical lens 8 which is closer to the LCD 10
is a transmitting/reflecting surface (half mirror).
An illumination light source 30 is a planar illumination light
source. When light emitted from the planar illumination light
source 30 enters the LCD 10, the cylindrical lens 8 has the role as
an illumination optical system.
In this embodiment, all surfaces constituting the optical elements
1 and 2 and the lens 5 have a plane-symmetric shape with respect to
a plane parallel to the sheet of FIG. 2A (yz-cross section) as the
only plane of symmetry.
The light emitted from the planar illumination light source 30 is
transmitted through a polarizing plate 14 to be converted into
linearly-polarized light and then is reflected by a surface S23 of
the cylindrical lens 8 to proceed to the LCD 10. The light
obliquely entering the LCD 10 and reflected by its image-displaying
surface in an oblique direction passes through the cylindrical lens
8 and then is transmitted through a polarizing plate 7 to enter the
lens 5. The functions of the polarizing plates 7 and 14 are the
same as those in Embodiment 1.
The light emerging from the lens 5 is transmitted through the
lenses 4 and 3 to enter the optical element 2. Furthermore, the
light is transmitted through the cemented surface of the optical
elements 2 and 1 to enter the optical element 1.
The light entering the optical element 1 from a surface B is
introduced to a surface C after being reflected on a surface A. The
light impinging on the surface C is subjected to the returning
reflection in an approximately opposite direction and then proceeds
inversely to the direction before the reflection on the surface C.
The light reflected on the surface C is again reflected on the
surface A, further again reflected on the surface B, emerges from
the optical element 1 from the surface A and then proceeds to an
exit pupil S1 through the lens 9.
A numerical example of this embodiment is shown in Table 2.
The unit of length in Table 2 is mm. Therefore, the optical system
shown in Table 2 is a display optical system that displays an image
whose size is about 18 mm.times.14 mm and horizontal field angle is
60.degree. at the infinite position in the direction of the
z-axis.
In this embodiment, an extremely large distortion is generated by
the optical system. Therefore, an image subjected to the electric
distorting processing (inverse-correction) in the direction inverse
to that of the distortion generated by the optical system is output
to the image display element. The output image (inversely-corrected
image) obtained by inversely correcting the input image (FIG. 7) is
shown in FIG. 2B.
The calculation of the low-pass filter effect for each of 8.times.8
regions in the output image distorted as shown in FIG. 2B can
obtain a region where the low-pass filter effect is high, a region
where the low-pass filter effect is middle and a region where the
low-pass filter effect is low, the calculation being performed
according to the above-mentioned setting condition of the low-pass
filter effect.
Thus, in this embodiment, the distortion is not corrected by the
optical system, so that the optical system can be configured so as
to contribute to corrections of various aberrations other than the
distortion and to miniaturization of the optical system. This
embodiment achieves a display optical system (that is, an image
display apparatus) having an extremely good optical performance and
thereby enabling to provide an image with reduced distortion while
its size is small.
Furthermore, employing the configuration capable of providing an
adequate low-pass filter effect for each region while distorting
the image output to the image display element can cause the
observer to observe a good image with reduced distortion, moire
fringe and aliasing when the observer observes the image display
element through the optical system.
TABLE-US-00002 TABLE 2 SURF X Y Z A R typ Nd .nu.d 1 0.000 0.000
0.000 0.000 0.0000 SPH 1.0000 0.0 2 0.000 0.354 18.405 1.469
-136.7211 SPH 1.7618 26.5 3 0.000 0.406 20.404 1.469 .infin. SPH
1.0000 4 0.000 9.259 21.177 2.214 -469.1111 FFS1 1.5300 55.8 5
0.000 5.022 38.481 -23.133 -75.5610 FFS2 -1.5300 55.8 6 0.000 9.259
21.177 2.214 -469.1111 FFS1 1.5300 55.8 7 0.000 34.209 54.410
55.179 -180.1511 FFS3 -1.5300 55.8 8 0.000 9.259 21.177 2.214
-469.1111 FFS1 1.5300 55.8 9 0.000 5.022 38.481 -23.133 -75.5610
FFS2 1.5300 55.8 10 0.000 5.022 38.481 -23.133 -75.5610 FFS2 1.5300
55.8 11 0.000 0.345 46.831 -31.122 -107.1944 FFS4 1.0000 12 0.000
-9.458 40.330 -64.394 19.9021 SPH 1.4875 70.2 13 0.000 -15.667
42.631 -60.135 -51.7320 SPH 1.0000 14 0.000 -16.654 42.682 -60.413
-40.0596 SPH 1.7618 26.5 15 0.000 -17.814 44.691 -63.011 65.9693
SPH 1.0000 16 0.000 -21.067 47.028 -63.163 18.8246 FFS5 1.5300 55.8
17 0.000 -36.301 33.494 -74.884 -77.6795 FFS6 1.0000 18 0.000
-34.770 53.842 -89.719 36.9295 CYL 1.4875 70.4 19 0.000 -36.670
53.819 -87.760 38.5518 CYL 1.0000 20 0.000 -49.906 54.337 -46.389
.infin. SPH 1.5500 52.0 21 0.000 -50.606 54.364 -46.389 .infin. SPH
1.0000 22 0.000 -50.606 54.364 -46.389 0.0000 SPH 1.0000 0.0 FFS1
c1: -3.5142e+000 c5: -1.1224e-003 c6: 3.0047e-004 c10: 1.6178e-006
c11: -2.3024e-006 c12: -1.0174e-007 c13: -1.3665e-007 c14:
-8.2428e-008 c20: 6.4444e-011 c21: -4.5295e-010 c22: -3.8790e-010
c23: 3.3132e-013 c24: 2.2972e-013 c25: 6.0295e-013 c26: 1.4337e-012
FFS2 c1: 1.2950e+000 c5: -1.4032e-003 c6: -2.7965e-004 c10:
7.0382e-006 c11: 5.5439e-007 c12: -1.7720e-008 c13: 5.3552e-009
c14: 1.8816e-007 c20: -8.0878e-010 c21: 5.5724e-010 c22:
-5.6967e-010 c23: -3.8603e-013 c24: -1.7807e-011 c25: -1.8045e-012
c26: -9.2497e-012 FFS3 c1: -5.9895e+000 c5: -8.9010e-004 c6:
-6.3693e-005 c10: 1.8175e-006 c11: 9.7146e-006 c12: 1.1339e-007
c13: 4.2958e-009 c14: 2.5671e-008 c20: 9.3576e-011 c21:
-3.8979e-010 c22: 3.1680e-009 c23: -2.7038e-011 c24: 7.7717e-012
c25: -1.0598e-011 c26: 5.4081e-012 FFS4 c1: 3.2848e+000 c5:
-1.3584e-003 c6: -3.6912e-003 c10: 6.8912e-005 c11: 4.0703e-005
c12: 6.8456e-007 c13: -3.2043e-007 c14: -3.3292e-007 c20:
-3.8440e-009 c21: -2.6745e-009 c22: 1.3757e-009 c23: -1.6929e-010
c24: -2.3522e-010 c25: -1.0763e-010 c26: -4.0575e-011 FFS5 c1:
-5.3753e-001 c5: 1.5035e-003 c6: -1.7174e-004 c10: 1.5884e-005 c11:
1.3331e-004 c12: -2.1151e-006 c13: 9.6711e-007 c14: -1.4211e-006
c20: -6.6002e-008 c21: 3.6230e-008 c22: -1.6300e-008 c23:
1.1167e-010 c24: -1.1552e-009 c25: 5.5383e-010 c26: -2.7815e-009
FFS6 c1: 6.7826e-001 c5: -3.6616e-003 c6: 6.1230e-005 c10:
-9.0367e-006 c11: -2.6342e-005 c12: 5.1808e-007 c13: 3.3044e-007
c14: -1.0194e-007 c20: -1.5907e-009 c21: 7.6035e-009 c22:
2.5169e-009 c23: 2.9829e-010 c24: -2.3108e-010 c25: 5.8907e-012
c26: 1.9299e-011
Embodiment 3
FIG. 3A shows the configuration of a display optical system for an
HMD that is Embodiment 3 of the present invention.
An optical element 1 is a prism member having three or more optical
surfaces on a transparent media whose refractive index is larger
than 1, and an optical element 2 is a prism member having two
optical surfaces on a transparent media whose refractive index is
larger than 1. Reference numerals 3 and 4 denote cemented lenses,
reference numeral 5 denotes a lens having two surfaces, and
reference numeral 8 denotes a decentered cylindrical lens.
Reference numeral 10 denotes an image display element (reflective
LCD).
A surface of the cylindrical lens 8 which is closer to the LCD 10
is a transmitting/reflecting surface (half mirror).
An illumination light source 30 is a planar illumination light
source. When light emitted from the planar illumination light
source 30 enters the LCD 10, the cylindrical lens 8 has the role as
an illumination optical system.
In this embodiment, all surfaces constituting the optical elements
1 and 2 and the lens 5 have a plane-symmetric shape with respect to
a plane parallel to the sheet of FIG. 3A (yz-cross section) as the
only plane of symmetry.
The light emitted from the planar illumination light source 30 is
transmitted through a polarizing plate 14 to be converted into
linearly-polarized light and then is reflected by a surface S23 of
the cylindrical lens 8 to proceed to the LCD 10. The light
obliquely entering the LCD 10 and reflected by its image-displaying
surface in an oblique direction passes through the cylindrical lens
8 and then is transmitted through a polarizing plate 7 to enter the
lens 5.
The light emerging from the lens 5 is transmitted through the
cemented lenses 4 and 3 to enter the optical element 2.
Furthermore, the light is transmitted through the cemented surface
of the optical elements 2 and 1 to enter the optical element 1.
The light entering the optical element 1 from a surface B is
introduced to a surface C after being reflected on a surface A. The
light impinging on the surface C is subjected to the returning
reflection in an approximately opposite direction and then proceeds
inversely to the direction before the reflection on the surface C.
The light reflected on the surface C is again reflected on the
surface A, further again reflected on the surface B, emerges from
the optical element 1 from the surface A and then proceeds to an
exit pupil S1.
A numerical example of this embodiment is shown in Table 3.
The unit of length in Table 3 is mm. Therefore, the optical system
shown in Table 3 is a display optical system that displays an image
whose size is about 18 mm.times.14 mm and horizontal field angle is
60.degree. at the infinite position in the direction of the
z-axis.
In this embodiment, an extremely large distortion is generated by
the optical system. Therefore, an image subjected to the electric
distorting processing (inverse-correction) in the direction inverse
to that of the distortion generated by the optical system is output
to the image display element. The output image (inversely-corrected
image) obtained by inversely correcting the input image (FIG. 7) is
shown in FIG. 3B.
The calculation of the low-pass filter effect for each of 8.times.8
regions in the output image distorted as shown in FIG. 3B can
obtain a region where the low-pass filter effect is high, a region
where the low-pass filter effect is middle and a region where the
low-pass filter effect is low, the calculation being performed
according to the above-mentioned setting condition of the low-pass
filter effect.
Thus, in this embodiment, the distortion is not corrected by the
optical system, so that the optical system can be configured so as
to contribute to corrections of various aberrations other than the
distortion and to miniaturization of the optical system. This
embodiment achieves a display optical system (that is, an image
display apparatus) having an extremely good optical performance and
thereby enabling to provide an image with reduced distortion while
its size is small.
Furthermore, employing the configuration capable of providing an
adequate low-pass filter effect for each region while distorting
the image output to the image display element can cause the
observer to observe a good image with reduced distortion, moire
fringe and aliasing when the observer observes the image display
element through the optical system.
TABLE-US-00003 TABLE 3 SURF X Y Z A R typ Nd .nu.d 1 0.000 0.000
0.000 0.000 0.0000 SPH 1.0000 0.0 2 0.000 10.841 21.436 -0.604
-352.9905 FFS1 1.5300 55.8 3 0.000 -2.791 33.876 -30.275 -75.8089
FFS2 -1.5300 55.8 4 0.000 10.841 21.436 -0.604 -352.9905 FFS1
1.5300 55.8 5 0.000 33.879 41.433 53.462 -197.0908 FFS3 -1.5300
55.8 6 0.000 10.841 21.436 -0.604 -352.9905 FFS1 1.5300 55.8 7
0.000 -2.791 33.876 -30.275 -75.8089 FFS2 1.5300 55.8 8 0.000
-2.791 33.876 -30.275 -75.8089 FFS2 1.5300 55.8 9 0.000 -7.196
41.839 -43.971 -63.4555 FFS4 1.0000 10 0.000 -11.638 37.392 -58.707
18.6660 SPH 1.4875 70.2 11 0.000 -22.246 43.841 -58.707 -22.2689
SPH 1.7618 26.5 12 0.000 -23.785 44.776 -58.707 61.7075 SPH 1.0000
13 0.000 -25.783 43.765 -48.028 21.0144 FFS5 1.5300 55.8 14 0.000
-41.494 26.775 -81.743 -92.5180 FFS6 1.0000 15 0.000 -38.685 45.914
-82.594 41.2870 CYL 1.4875 70.2 16 0.000 -40.878 44.746 -80.774
41.2870 CYL 1.0000 17 0.000 -55.794 47.169 -54.561 .infin. SPH
1.5500 52.0 18 0.000 -56.485 47.281 -54.561 .infin. SPH 1.0000 19
0.000 -56.485 47.281 -54.561 0.0000 SPH 1.0000 0.0 FFS1 c1:
7.2184e+001 c5: -1.6665e-003 c6: -7.2422e-005 c10: -4.6772e-006
c11: -1.2027e-005 c12: -2.5677e-007 c13: -4.8083e-007 c14:
-2.5025e-007 c20: -2.3618e-010 c21: 6.1664e-011 c22: 3.8390e-010
c23: 4.3369e-011 c24: 6.6350e-011 c25: 8.8166e-011 c26: 4.8625e-011
FFS2 c1: -2.6318e-001 c5: -1.1855e-003 c6: -3.6956e-004 c10:
-6.9695e-006 c11: -1.0001e-006 c12: -1.6620e-009 c13: -1.1802e-007
c14: 2.9418e-008 c20: 8.8307e-010 c21: 5.1973e-010 c22:
-4.6161e-010 c23: 2.1291e-013 c24: -1.7111e-012 c25: 6.2447e-012
c26: -4.4093e-012 FFS3 c1: -6.6986e+001 c5: 1.0045e-004 c6:
-1.1422e-003 c10: 7.4597e-006 c11: -2.2377e-005 c12: 1.7250e-006
c13: -1.5586e-006 c14: 9.6682e-007 c20: -4.4616e-008 c21:
3.7490e-008 c22: -2.3601e-008 c23: -3.7207e-010 c24: 9.9407e-011
c25: -3.6052e-010 c26: 7.2921e-011 FFS4 c1: -6.5653e+000 c5:
-2.1549e-004 c6: -6.3543e-003 c10: 6.1509e-005 c11: 5.1806e-005
c12: -2.6789e-007 c13: 1.5006e-008 c14: -6.0216e-007 c20:
-1.9440e-008 c21: -7.7214e-009 c22: 2.8584e-009 c23: 1.5916e-010
c24: 4.7203e-010 c25: -4.3913e-010 c26: -1.4201e-010 FFS5 c1:
-2.2697e-001 c5: 5.5284e-004 c6: -8.9698e-005 c10: -3.5449e-005
c11: 7.2729e-005 c12: -2.1230e-006 c13: 1.4771e-006 c14:
-2.5204e-006 c20: 2.2693e-008 c21: -5.3195e-008 c22: -2.1732e-009
c23: 4.1625e-010 c24: -5.0053e-010 c25: 1.1931e-009 c26:
-2.8094e-009 FFS6 c1: -2.5783e+001 c5: 1.9452e-003 c6: 1.2450e-003
c10: -2.5389e-005 c11: -1.6737e-004 c12: 4.7165e-006 c13:
1.5333e-006 c14: -9.3819e-008 c20: -3.2552e-009 c21: 3.1982e-008
c22: 1.3708e-008 c23: 3.2537e-010 c24: -2.7285e-010 c25:
-1.2959e-010 c26: 3.0139e-011
Embodiment 4
FIG. 4A shows the configuration of a display optical system for an
HMD that is Embodiment 4 of the present invention.
An optical element 1 is a prism member having three or more optical
surfaces on a transparent media whose refractive index is larger
than 1. Reference numerals 3, 4, and 6 denote lenses each having
two surfaces. Reference numeral 10 denotes an image display element
(reflective LCD). In this embodiment, an illumination light source
is not shown.
In this embodiment, all surfaces constituting the optical elements
1 have a plane-symmetric shape with respect to a plane parallel to
the sheet of FIG. 4A (yz-cross section) as the only plane of
symmetry.
The light emerging from the image display element 10 is transmitted
through the lenses 6, 4, and 3 to enter the optical element 1 from
a surface C. The light entering the optical element 1 is reflected
on a surface B after being reflected on a surface A, and then
emerges from the optical element 1 from the surface A to proceed to
an exit pupil S1.
A numerical example of this embodiment is shown in Table 4.
The unit of length in Table 4 is mm. Therefore, the optical system
shown in Table 4 is a display optical system that displays an image
whose size is about 18 mm.times.14 mm and horizontal field angle is
60.degree. at the infinite position in the direction of the
z-axis.
In this embodiment, an extremely large distortion is generated by
the optical system. Therefore, an image subjected to the electric
distorting processing (inverse-correction) in the direction inverse
to that of the distortion generated by the optical system is output
to the image display element. The output image (inversely-corrected
image) obtained by inversely correcting the input image (FIG. 7) is
shown in FIG. 4B.
The calculation of the low-pass filter effect for each of 8.times.8
regions in the output image distorted as shown in FIG. 4B can
obtain a region where the low-pass filter effect is high, a region
where the low-pass filter effect is middle and a region where the
low-pass filter effect is low, the calculation being performed
according to the above-mentioned setting condition of the low-pass
filter effect.
Thus, in this embodiment, the distortion is not corrected in the
optical system, so that the optical system can be configured so as
to contribute to corrections of various aberrations other than the
distortion and to miniaturization of the optical system. This
embodiment achieves a display optical system (that is, an image
display apparatus) having an extremely good optical performance and
thereby enabling to provide an image with reduced distortion while
its size is small.
Furthermore, employing the configuration capable of providing an
adequate low-pass filter effect for each region while distorting
the image output to the image display element can cause the
observer to observe a good image with reduced distortion, moire
fringe and aliasing when the observer observes the image display
element through the optical system.
TABLE-US-00004 TABLE 4 SURF X Y Z A R typ Nd .nu.d 1 0.000 0.000
0.000 0.000 0.0000 SPH 1.0000 0.0 2 0.000 14.451 20.154 -1.074
-718.3837 FFS1 1.5300 55.8 3 0.000 -2.366 35.080 -30.181 -72.6014
FFS2 -1.5300 55.8 4 0.000 14.451 20.154 -1.074 -718.3837 FFS1
1.5300 55.8 5 0.000 38.725 48.761 28.404 -69.8715 FFS3 1.0000 6
0.000 57.966 42.294 49.155 4400.3327 SPH 1.6775 31.6 7 0.000 77.413
59.108 53.609 -41.8639 SPH 1.0000 8 0.000 82.841 56.549 51.868
30.0884 SPH 1.5769 62.8 9 0.000 89.294 61.614 54.919 -332.5298 SPH
1.0000 10 0.000 90.995 62.089 54.463 17.0171 SPH 1.5633 63.7 11
0.000 95.850 68.175 52.535 39.9059 SPH 1.0000 12 0.000 108.390
77.785 79.641 0.0000 SPH 1.0000 0.0 FFS1 c1: -6.6774e+002 c5:
-6.6762e-004 c6: 1.2170e-004 c10: -1.3837e-005 c11: -2.2316e-005
c12: 1.0432e-007 c13: 2.9061e-008 c14: -8.8845e-008 FFS2 c1:
-1.9853e+000 c5: -1.3309e-003 c6: -6.6634e-004 c10: -4.4072e-006
c11: -2.7890e-006 c12: -5.2049e-008 c13: -1.0060e-010 c14:
4.6680e-008 c20: 1.6059e-010 c21: -1.0975e-010 c22: 5.7038e-010
c23: -4.6867e-012 c24: 3.5001e-012 c25: 2.3136e-013 c26:
-3.8790e-012 FFS3 c1: -6.5731e-001 c5: -6.0265e-003 c6: 8.1242e-004
c10: -1.5245e-004 c11: -6.2679e-005 c12: 1.8282e-006 c13:
2.3303e-006 c14: -7.2543e-007 c20: 3.6365e-009 c21: 3.7097e-008
c22: 1.2747e-008 c23: 2.3783e-010 c24: -2.5087e-010 c25:
-4.6163e-010 c26: 4.8817e-010
Embodiment 5
FIG. 5A shows the configuration of a display optical system for an
HMD that is Embodiment 5 of the present invention.
An optical element 1 is a prism member having three or more optical
surfaces, which are a surface A, a surface B, a surface C and a
surface D, on a transparent media whose refractive index is larger
than 1. Optical elements 2 and 3 are prism members each having two
optical surfaces on a transparent media whose refractive index is
larger than 1. Reference numerals 4 and 5 denote lenses each having
two surfaces; these lenses 4 and 5 are cemented with each other.
Reference numeral 10 denotes an image display element (reflective
LCD). In this embodiment, an illumination light source is not
shown.
In this embodiment, all surfaces constituting the optical elements
1, 2 and 3 have a plane-symmetric shape with respect to a plane
parallel to the sheet of FIG. 5A (yz-cross section) as the only
plane of symmetry.
The light emerging from the image display element 10 is transmitted
through the lenses 5 and 4 and the optical elements 3 and 2 to
enter the optical element 1 from a surface D. The light entering
the optical element 1 is reflected on a surface A after being
reflected on a surface C, further reflected on a surface B, and
then emerges from the optical element 1 from the surface A to
proceed to an exit pupil S1.
A numerical example of this embodiment is shown in Table 5.
The unit of length in Table 5 is mm. Therefore, the optical system
shown in Table 5 is a display optical system that displays an image
whose size is about 18 mm.times.14 mm and horizontal field angle is
60.degree. at the infinite position in the direction of the
z-axis.
In this embodiment, an extremely large distortion is generated by
the optical system. Therefore, an image subjected to the electric
distorting processing (inverse-correction) in the direction inverse
to that of the distortion generated by the optical system is output
to the image display element. The output image (inversely-corrected
image) obtained by inversely correcting the input image (FIG. 7) is
shown in FIG. 5B.
The calculation of the low-pass filter effect for each of 8.times.8
regions in the output image distorted as shown in FIG. 5B can
obtain a region where the low-pass filter effect is high, a region
where the low-pass filter effect is middle and a region where the
low-pass filter effect is low, the calculation being performed
according to the above-mentioned setting condition of the low-pass
filter effect.
Thus, in this embodiment, the distortion is not corrected in the
optical system, so that the optical system can be configured so as
to contribute to corrections of various aberrations other than the
distortion and to miniaturization of the optical system. This
embodiment achieves a display optical system (that is, an image
display apparatus) having an extremely good optical performance and
thereby enabling to provide an image with reduced distortion while
its size is small.
Furthermore, employing the configuration capable of providing an
adequate low-pass filter effect for each region while distorting
the image output to the image display element can cause the
observer to observe a good image with reduced distortion, moire
fringe and aliasing when the observer observes the image display
element through the optical system.
TABLE-US-00005 TABLE 5 SURF X Y Z A R typ Nd .nu.d 1 0.000 0.000
0.000 0.000 0.0000 SPH 1.0000 0.0 2 0.000 6.001 22.661 -3.015
-244.6358 FFS1 1.5300 55.8 3 0.000 -5.783 35.586 -34.841 -63.4009
FFS2 -1.5300 55.8 4 0.000 6.001 22.661 -3.015 -244.6358 FFS1 1.5300
55.8 5 0.000 33.742 51.816 16.395 -134.9399 FFS3 -1.5300 55.8 6
0.000 52.536 20.599 -6.691 59.4225 FFS4 -1.0000 7 0.000 61.922
14.511 -11.271 62.2478 FFS5 -1.5709 33.8 8 0.000 60.404 2.242
-14.204 143.5896 FFS6 -1.0000 9 0.000 64.966 -2.985 -14.247
-37.9321 FFS7 -1.5300 55.8 10 0.000 72.989 -18.039 -11.670 54.1602
FFS8 -1.0000 11 0.000 69.302 -20.684 -11.670 -25.7628 SPH -1.6125
60.7 12 0.000 72.478 -31.079 -11.670 22.2050 SPH -1.7552 27.6 13
0.000 72.838 -32.824 -11.670 183.0353 SPH -1.0000 14 0.000 77.668
-56.210 -15.137 0.0000 SPH -1.0000 0.0 FFS1 c1: 2.5709e+001 c5:
-2.2951e-003 c6: -1.2671e-003 c10: -9.0272e-006 c11: -2.6018e-005
c12: 2.6016e-007 c13: -1.8366e-007 c14: -1.1967e-007 c20:
-1.5225e-009 c21: 1.5850e-010 c22: 3.4085e-009 c23: 2.9938e-012
c24: -2.2093e-011 c25: -1.6024e-011 c26: 8.0489e-012 FFS2 c1:
-2.7121e-001 c5: -1.1914e-003 c6: -5.1007e-004 c10: 3.3657e-006
c11: -2.4642e-006 c12: -3.2679e-008 c13: -2.4434e-008 c14:
-3.3506e-008 c20: 6.6519e-010 c21: -4.4056e-010 c22: 4.4458e-010
c23: 4.3419e-012 c24: -3.1794e-012 c25: -5.4346e-013 c26:
-3.8402e-012 FFS3 c1: 6.0381e-001 c5: -1.0115e-004 c6: 2.0574e-004
c10: 2.3999e-007 c11: -7.8454e-006 c12: 2.5931e-008 c13:
2.0375e-009 c14: 1.9470e-009 c20: -2.2269e-012 c21: 1.5218e-010
c22: -9.4066e-010 c23: -2.6234e-011 c24: -3.0703e-012 c25:
3.0102e-012 c26: -8.9320e-013 FFS4 c1: -2.7539e+000 c5: 7.1799e-004
c6: -2.6347e-003 c10: 5.5003e-006 c11: -1.7782e-006 c12:
-1.3269e-007 c13: -5.0486e-007 c14: -2.0578e-007 c20: -4.5659e-009
c21: -1.2435e-008 c22: -1.5262e-008 c23: 6.1551e-010 c24:
-1.2093e-010 c25: 4.7333e-010 c26: -2.1595e-010 FFS5 c1:
7.2268e-001 c5: 9.7360e-004 c6: 1.4458e-003 c10: -8.9127e-005 c11:
4.1840e-005 c12: -2.3570e-006 c13: -1.1168e-006 c14: 6.5803e-007
c20: -6.8198e-005 c21: -5.3553e-009 c22: -1.1075e-007 c23:
8.3682e-010 c24: 4.3730e-010 c25: 4.8670e-010 c26: 3.9744e-010 FFS6
c1: -1.1040e+001 c5: -3.7530e-004 c6: -5.7247e-004 c10: 3.5336e-006
c11: -3.4104e-005 c12: -1.0482e-007 c13: 5.3276e-007 c14:
-2.8062e-007 c20: 8.5614e-009 c21: 2.1113e-011 c22: -3.9658e-008
c23: -2.9025e-010 c24: 3.9761e-010 c25: -1.7519e-011 c26:
-4.7418e-011 FFS7 c1: 1.7736e-001 c5: -2.0250e-003 c6: 1.0966e-004
c10: 4.7470e-005 c11: -3.9099e-005 c12: 9.8450e-008 c13:
2.2094e-007 c14: 2.9521e-007 c20: 2.6216e-008 c21: -2.3300e-009
c22: 1.8448e-008 c23: -6.4972e-010 c24: 2.4594e-010 c25:
-5.1593e-010 c26: 1.8772e-010 FFS8 c1: -2.7775e+000 c5:
-4.0966e-004 c6: 3.3381e-004 c10: -1.0575e-005 c11: -1.2205e-005
c12: 2.9793e-007 c13: -1.4652e-006 c14: 5.6747e-007 c20:
6.8063e-008 c21: -1.0022e-008 c22: 2.0087e-008 c23: -2.5509e-010
c24: 1.3135e-010 c25: -1.5838e-010 c26: 5.5155e-010
According to each of the above-described embodiments, when
performing the electric distorting processing (inverse-correction)
for the input image, an adequate low-pass filter effect can be set
depending on the relationship of the number of pixels in a specific
region before and after the distorting processing. Therefore,
generation of the moire fringe can be reduced while suppressing
deterioration of resolution.
Furthermore, the present invention is not limited to these
embodiments and various variations and modifications may be made
without departing from the scope of the present invention.
This application claims foreign priority benefits based on Japanese
Patent Application No. 2006-236439, filed on Aug. 31, 2006, which
is hereby incorporated by reference herein in its entirety as if
fully set forth herein.
* * * * *